Biting or drinking something cold, hot, sweet, or sour may elicit a sharp, lancinating pain in a tooth, and such a pain is believed to arise from a stimulus to the dentinal nerves of the tooth. A huge number of dentinal tubules extend through tooth dentin, and the interior of the dentinal tubules is full of tissue fluid. A tooth with exposed dentin is thought to experience pain as follows: An external stimulus forces the tissue fluid in the dentinal tubules to move and consequently stimulate sensory nerves in the vicinity of the boundary between the dental pulp and dentin. Such a stimulus can be caused by anything that can cause movement of the tissue fluid in the dentinal tubules. This means that dentinal pain can be elicited by any of mechanical or thermal stimuli, sweetness, sourness, and stimuli that induce a change in osmotic pressure. The pain therefore occurs, for example, during eating, drinking, brushing with a toothbrush, and exercise, thus significantly affecting the daily life. The types of dentinal hypersensitivity include: cervical hypersensitivity associated with defective enamel or cementum resulting from causes such as dental caries and tooth abrasion due to improper brushing with a toothbrush; and root hypersensitivity associated with phenomena such as gingival recession due to improper brushing. In recent years, the population is increasingly aging and storage of vital teeth is attracting a growing attention. This produces an increasing trend in the prevalence of dentinal hypersensitivity attributed to gingival recession or root exposure.
Most of treatment techniques currently employed against dentinal hypersensitivity are intended to inhibit the movement of the tissue fluid in the dentinal tubules. Examples of techniques for blocking external stimuli with the use of various materials include: (1) mechanical covering of exposed dentin surface with a resin material or glass ionomer cement; (2) occlusion of tubules with a reaction product of oxalic acid with calcium contained in dentin; and (3) occlusion of tubules with intratubular protein coagulated by glutaraldehyde.
The above conventional techniques, however, have a disadvantage in that the materials used have a low pH or in that the materials are highly toxic and are not safe to use for treating subgingival areas or interdental areas. In addition, dentinal tubule occlusion accomplished by the conventional techniques unfortunately fails to remain intact and maintain its effect in an oral environment. To solve these problems, the following techniques using calcium phosphate have recently been disclosed.
Patent Literature 1 describes a composition for use against dentinal hypersensitivity that is capable of prevention and treatment of dentinal hypersensitivity, the composition including particles of hydroxyapatite or tricalcium phosphate that have a particle diameter of 1.0 μm to 5.0 μm. However, unfortunately, this composition is incapable of achieving secure occlusion of dentinal tubules, due to lacking inorganic particles (B) having an average particle diameter of 0.6 to 10 μm and reactive with water to form apatite (the inorganic particles (B) are essential for the present invention), and fails to achieve durable dentinal tubule occlusion.
Patent Literature 2 describes a dentinal tubule occlusion material that is characterized by containing calcium phosphate particles not larger than 900 nm. This literature alleges that the material can reliably fill the interior of dentinal tubules and that the calcium phosphate particles filling the interior of the dentinal tubules can act as cores to promote remineralization. However, with the mere use of small calcium phosphate particles not larger than 900 nm, dissolution of particles with a large specific surface area proceeds more readily than mineralization in the oral environment, which leads not only to failure of secure initial physical occlusion but also to post-occlusion detachment of the occlusion product due to physical stimuli such as those given by gargling, eating, and drinking. Furthermore, the dentinal tubule occlusion material is neither capable of achieving secure occlusion of dentinal tubules nor capable of achieving durable dentinal tubule occlusion.
Patent Literature 3 describes a two-pack type dentinal tubule occlusion material that is characterized by including a component containing tetracalcium phosphate particles and an alkali metal phosphate and a component containing water and by undergoing conversion to hydroxyapatite as a result of mixing of the two components. This occlusion material is capable of depositing hydroxyapatite deep into dentinal tubules and achieving secure occlusion of the dentinal tubules. However, such a two-pack type material requires the practitioner to perform material preparation each time he/she uses it. If provided in the form of an one-pack type material, the occlusion material is unsatisfactory in terms of storage stability or resistance of dentinal tubule occlusion to acids.
Patent Literature 4 describes a two-pack type dentinal tubule occlusion material that includes a component containing poorly-soluble calcium phosphate particles and a phosphorus-free calcium compound and a component containing water and that undergoes gradual conversion to hydroxyapatite as a result of mixing of the two components. This occlusion material is excellent in terms of initial degree of dentinal tubule occlusion and durability of dentinal tubule occlusion. However, such a two-pack type material requires the practitioner to perform material preparation each time he/she uses it. If provided in the form of an one-pack type material, the occlusion material is unsatisfactory in terms of storage stability or resistance of dentinal tubule occlusion to acids.
That is, conventional dentinal tubule occlusion materials as disclosed in Patent Literatures mentioned above are those which cannot provide a sufficient initial degree of dentinal tubule occlusion, those which have a disadvantage in terms of durability of dentinal tubule occlusion, those which require material preparation each time they are used, or those which, when provided in the form of an one-pack type material, are unsatisfactory in terms of storage stability or resistance of dentinal tubule occlusion to acids.